1. Field of the Invention
The present invention relates to a method of producing maltose, wherein a liquefied starch is saccharified by an amylase produced by a strain of streptomyces and a .beta.-amylase. Maltose is a disaccharide in which two molecules of D-glucose are combined with each other by .alpha.-linkage, being white powder or crystal extremely soluble in water, having delicious sweetness the degree of which is 1/2 to 1/3 that of sucrose.
Maltose is used as a sweetening agent having characteristics with which sucrose is not endowed sucrose and; also maltose can be used in various fields such as for a culture medium in the fermentation industries and a material for producing derivatives such as maltitol and the like.
2. Prior Art
Conventionally, .beta.-amylase and isoamylase and/or pullulanase have been employed as indispensable enzymes and .beta.-amylase has been used generally in the liquefying process in the industrial production of maltose enzymatically. Maltose and maltotriose are mainly contained in the substance which is produced by the combined action of these enzymes, and the yield of the maltotriose is influenced by the extent of the action of .alpha.-amylase. Maltotriose can not or can hardly hydrolyzed practically, as is well known, by any one of the foregoing three enzymes. It is required, therefore, for obtaining a substance with a higher content of maltose, to lessen the amount of maltotriose produced, as far as possible in the production by the enzymatic saccharization method. Indeed, when saccharification of starch was carried out by using a combination of .alpha.-amylase and .beta.-amylase, the content of maltose in the product at most amounted to 40 to 70%. In order to obtain a higher yield of maltose, a liquefied starch having markedly low dextrose equivalent has been prepared by controlling the action of .alpha.-amylase in the liquefying process of the starch or by mechanically liquefying the starch, and the resultant liquefied starch has been saccharized by, e.g., .beta.-amylase and isoamylase. The liquefied starch with low dextrose equivalent, however, is apt to retrogradate, and the higher the concentration the greater the degree of retrogradation. The production of the substance containing a high content of maltose can not be easily carried out in a higher concentration of starch and usually, it may preferably be carried out under such an industrially disadvantageous condition as a low concentration of starch.
Furthermore, because of the low thermal stability of the isoamylase which has been commonly used in the industrial process, saccharifying temperature is at most in the range 50.degree. to 55.degree. C for the saccharification method using a combination of .beta.-amylase and isoamylase, and this is liable to cause a high possibility of contamination in the saccharification process; therefore, such a method employing these enzymes is disadvantageous in an industrial process.